The present invention relates generally to an apparatus, system, and method for measuring and transferring the contents of a vessel. In particular, the system relates to a system where an inner vessel containing a fluid is suspended in an outer vessel containing a fluid. The amount of fluid contained in the inner vessel is determined based upon the weight or buoyancy of the inner vessel within the outer vessel. The apparatus utilizes a sensing mechanism to determine the weight of the vessel.
Industries such as the semiconductor, fiber optics and pharmaceutical industries, among others, utilize processes which rely on highly accurate dispensation of materials, such as liquid or vapor chemicals. For instance, in the semiconductor industry, circuit manufacture involves numerous processing steps. Many of the processing steps involve the deposition of a material layer onto a semiconductor topography. These layers may be applied utilizing the deposition of a chemical vapor onto the surface of the semiconductor. Other film deposition techniques involve applying films by evaporation or sputtering. Chemical vapor deposition involves exposing the surface to gases, known as precursors, which undergo a chemical reaction to form a desired material on the surface.
Vapor deposition generally includes a liquid delivery or injection system for vaporizing a liquid chemical and carrying the vaporized liquid into the deposition process or reaction chamber for semiconductor processing. A typical liquid delivery process manages the flow of a liquid precursor or reagent, a carrier gas, and possibly one or more other gases. The liquid precursor is provided in a vaporization device and the carrier gas is delivered to the vaporization device for mixing with the vaporized liquid precursor.
The vapors or precursors are often produced in sealed containers, which have an input and output. The input carries gas into and near the bottom of the sealed container. The gas then bubbles up through the liquid. The gas combines with the liquid to form a vapor such that the upper portion of the sealed container is filled with the vapor. The output carries the vapor out of the sealed container for use in applying the material to a surface, such as a semiconductor surface.
Historically, volume measurement and flow control have been employed to achieve a desired dispensation volume or flow rate. Ever increasing demands driven by tighter delivery tolerances, material costs and waste management place greater demands on volume measurement methodologies. The volume of a given substance of otherwise constant mass can be influenced by temperature, pressure and dissolved gases. Dispensation device manufacturer""s must employ highly advanced and costly measures to compensate for and/or minimize induced errors by such influences. For instance, the effect of dissolved gases is readily evident when viewed through the clear acrylic of conventional liquid micro-balances, where large bubbles accumulate on the inner wall of the float vessel. Manufacturers of precision metering systems must include a pre-dispense degassing operation, as well as tightly controlled fluid temperature and pressure.
There are numerous techniques for measuring the level of liquid in a vessel. Some common techniques for sensing liquid level include: 1) weighing the container, 2) determining a differential pressure, 3) utilizing a float, optical, or acoustic sensor, and 4) utilizing a capacitive proximity switch. These sensor technologies provide either switched or variable outputs, where switching sensors provide a single dry contact switch output, and variable sensors provide a voltage output, corresponding to the operating range of the sensor.
There are enumerable fluid handling and control applications that utilize a variety of sensor technologies to detect the presence, availability, and/or amount of a liquid. Most liquid delivery systems rely on a source, or buffer supply, of liquid. In many applications liquid level and flow control technologies are connected to the source vessel(s) to detect the availability, amount, and rate of liquid to be delivered from the vessel.
A common method of liquid measurement and control is to position a plurality of switching sensors at various elevations on a source vessel. Each sensor performs a switching function to control the operating state of the fluid handling system. For example, if a low liquid level sensor on the source vessel is switched, a valve may be actuated to refill the source vessel until the liquid level reaches a high liquid level sensor, which would, in turn, switch the refill valve to the closed position. In some cases, a pair of sensors may be utilized to supply a specific amount of liquid to a point of use, where the distance between the sensors corresponds to a volume of liquid. Although sensors can be repositioned to change the amount of liquid to be dispensed, the configuration does not lend itself well to applications that require variable amounts or rates of liquid delivery.
Another common method of liquid measurement and control is to place the vessel onto a load cell, appropriately sized to measure the weight of the vessel and its liquid contents. This method features variable signal output based on the weight of the liquid in the vessel at any liquid level. The signal output can be monitored by a controller, which in turn, can perform fluid control functions based on programmed signal set points. This measurement technique can provide real time measurement and control of the liquid contained in the vessel, and is widely used for automated liquid delivery. However, the range and sensitivity of the scale can affect its size, accuracy, and cost.
Another common measurement technique employs load cells (scales) to monitor mass transfer operations. In applications demanding repeatable accuracy, costly measures must be taken to control external influences, such as isolation from air currents, subtle vibrations, and interconnecting system transients.
Some types of sensors must be in direct contact with the liquid. Other types are positioned above the surface of the liquid. Still other sensors are positioned outside the vessel along the vertical axis of the fluid column height. Load cells are positioned underneath the liquid vessel. For most high purity liquid delivery applications, it is preferred that the sensors not be in contact with, or in the contained environment of the liquid being delivered.
Due to the various chemical characteristics or fluid dynamic conditions, some sensors may not be suitable for use. For example, optical sensors may be compromised by reflectivity of the liquid or deposits on the sensor tip. Acoustic sensors may be compromised by sound wave interference or distortion during the signal transmission. In fact, some liquid applications operate in a vacuum environment where sound waves will not travel. Capacitive sensors can xe2x80x9cdriftxe2x80x9d from their calibrated electrical potential, and give false readings. Float sensors can fail mechanically and provide only fixed liquid level signals. Although these measurement and control techniques are very mature, they lack the ability to dynamically, and in real time, indicate liquid level and weight with a high degree of accuracy and repeatability.
Hall-effect sensors have been used to measure liquid levels. An example of such sensors is disclosed in U.S. Pat. No. 5,636,548. Buoyant vessel position monitoring has been used, as described in U.S. Pat. No. 5,606,109, for liquid volume deviation determinations. Prior devices teach volume measurement and compensation based on changes in temperature.
It is desirable to provide a system that provides improvements over prior art measurement techniques that are both efficient and cost effective.
The present invention relates to a fluid handling apparatus, a dispensing system, and a method for measuring and controlling the amount of fluid within a fluid handling apparatus. The fluid handling apparatus includes a containment vessel, a float vessel, and a sensor. The containment vessel has at least one inlet connected to a supply source for filling the containment vessel with a first material. The float vessel is disposed within the containment vessel and has at least one opening for receiving a second material. At least a portion of the second material is used for another purpose during operation of the fluid handling apparatus. The sensor is associated with the containment vessel for sensing the position of the float vessel within the containment vessel. The sensor is electronically connected to an indicator for transmitting a signal corresponding to a change in distance of the float vessel relative to the sensor and the change in distance is correlated with a weight of the float vessel.
In one embodiment, the indicator is a voltage indicator and the signal is voltage. The float vessel may include a magnet for interacting with the sensor to determine the position of the float vessel within the containment vessel. The sensor may be positioned substantially along a lower surface of the containment vessel and the sensed member may be a magnet. The magnet may be positioned inside a wall of the float vessel and the sensor is positioned inside a wall of the containment vessel such that the magnet and sensor are sealed from the first and second materials.
The fluid handling apparatus may include a centering device positioned inside the float vessel. The centering device may be used to maintain the float vessel substantially along a longitudinal axis of the containment vessel. In one embodiment, the containment vessel may be substantially sealed.
The fluid dispensing system includes a controller, an outer vessel, a float vessel, a sensor, and an input mechanism. The outer vessel holds a first fluid and the float vessel is positioned inside the outer vessel and holds a second fluid. The first and second fluids may be of the same type or different. The sensor is associated with the outer vessel and the controller is for monitoring a change in position of the float vessel within the outer vessel. A change in position is correlated with a weight of the second fluid within the float vessel. The input mechanism is associated with both the controller and a source for supplying a substance to the float vessel.
The substance may be a gas and the input mechanism may be a valve that is connected to a passageway, with the passageway positioned in the float vessel and having an end that is positioned beneath a surface of the second fluid to allow the gas to escape into the second fluid. The escaping gas becomes humidified as it passes through the second fluid and the system further comprises an outlet for the exit of the humidified gas.
A heat source may be positioned inside the float vessel and extend below the surface of the second liquid. An output is provided in the outer vessel and the second fluid vaporizes when in contact with the heating element. Vaporized fluid exits the outer vessel through the output.
Alternatively, or in addition thereto, the substance may be a second fluid that is periodically withdrawn from or replenished into the float vessel. The input mechanism may be a valve that is openable and closable to allow the second fluid to periodically flow into the float vessel, with operation of the valve being governed by the controller. The controller utilizes signals generated by the sensor in determining whether to open or close the valve. A weight of the second fluid is dynamically calculated based upon a sensed reading of the change in position of the float vessel within the outer vessel.
The float vessel may include a sensed member for interacting with the sensor in determining the position of the float vessel relative to the outer vessel. The sensed member may be a magnet and the sensor is connected to a voltage indicator to monitor the position of the magnet relative to the sensor. The sensor substantially simultaneously transmits a voltage to the controller that corresponds to the position of the magnet relative to the sensor. The controller determines, based upon this position, whether fluid should be input to the float vessel.
The outer vessel and float vessel include a head space positioned above the second fluid in the float vessel. The input mechanism includes a gas line positioned inside the head space, a gas source associated with the gas line, and a gas valve positioned along the gas line for starting and stopping the flow of gas from the gas source into the head space. The controller opens the gas valve to permit gas to fill the head space of the outer vessel and float vessel. The gas valve also permits gas to pressurize the head space.
The input mechanism may also include a fluid dispense line and a fluid supply valve. The fluid dispense line has an opening at one end, with the opening positioned below the surface of the second fluid in the float vessel and extending through the outer vessel at the other end. The fluid supply valve is opened by the controller to permit the second fluid to enter the float vessel and to close the fluid supply valve. During dispensing of the second fluid, the sensor monitors the position of the float vessel to determine when to close the fluid supply valve. When the sensor reads a low fluid level in the float vessel, the controller closes the gas valve and opens the fluid supply valve to dispense the second fluid into the float vessel. The second fluid may be dispensed into the float vessel from the fluid dispense line under pressure.
It is preferred that a useable volume of second fluid within the float vessel corresponds to a signal range of the sensor. The second fluid may include at least one fluid.
The method according to one embodiment of the invention is for measuring and controlling the amount of fluid within a fluid handling apparatus having a containment vessel and a float vessel. The float vessel is positioned inside the containment vessel. The method includes filling the containment vessel with a first fluid to cause the float vessel to float within the first fluid, filling the float vessel with a second fluid to create a usable volume of second fluid within the float vessel, measuring the change in position of the float vessel relative to a sensor in the containment vessel to determine when to fill and stop filling the float vessel with a second fluid, and performing an application to use at least a portion of the second fluid in the float vessel.
The method also may include refilling the float vessel with a second fluid to maintain a volume of second fluid based upon the measured position of the float vessel within the containment vessel. The sensor may read a distance between the sensor and the float vessel, with the signal from the sensor being an indicated voltage and the change in indicated voltage being calculated based upon the last reading. The method may also include converting the change in indicated voltage into a weight of the second fluid within the float vessel, wherein the weight of the second fluid is utilized to determine whether to input the second fluid into the float vessel.
In one embodiment, the method includes bubbling a gas through the second fluid in order to generate a humidified gas and dispensing the humidified gas through an outlet defined in the containment vessel. In another embodiment, the method includes heating the second liquid with a heating element in order to generate a vaporized liquid and dispensing the vaporized liquid through an outlet defined in the containment vessel.